1. Field of the Invention
The present invention generally relates to ion implantation, and more particularly, to an ion implanter and a method for adjusting a shape of an ion beam with a simple mechanism and relatively low cost.
2. Description of the Prior Art
Ion implantation processes are widely used in semiconductor manufacture, for example, to implant wafers with various ions having desired energy. Ion implantation processes typically require a uniform and consistent amount of ions to be implanted into a semiconductor wafer.
A conventional ion implanter includes at least an ion source and an analyzer magnet unit (AMU). The ion source is used to generate an ion beam. The ion beam generated from the ion source is analyzed by the AMU before the required ions are implanted into a wafer. Although the ion beam is analyzed by the AMU, the shape (cross-sectional shape) of the ion beam usually is not perfect as required. For different applications, the shape required for the ion beam usually varies. Different implantation parameters usually correspond to different required shapes; for example, a spot-shape and a line-shape are used for different implantation parameters.
Some prior art devices achieve these different beam-shape requirements by amending the designs of the ion source and/or the AMU, such that ion beams outputted from the AMU can almost, even perfectly, have the required shapes. However, implementation of the technology is difficult, and usually requires a complex mechanism and a high cost.
On the other hand, some prior art devices achieve the beam-shape requirement by applying a magnetic field, or an electromagnetic field, to change the motion trajectories of ions, such that the shape of the ion beam 10 is changed. Here, after an ion beam is outputted from the AMU, the magnetic field is applied to further adjust the shape of the ion beam. As shown in FIG. 1A, a conventional ion implanter typically includes an ion source 110, an AMU 120, a first bar magnet 131, and a second bar magnet 132. The ion beam 10 is generated by the ion source 110 and adjusted by the AMU 120 before it is injected into a wafer 20. Herein, the first bar magnet 131 and the second bar magnet 132 are separately located on opposing sides of the trajectory of the ion beam 10 and used to adjust the shape of the ion beam 10.
FIG. 1B shows an example of the first bar magnet 131 and the second bar magnet 132 being located on opposite sides of the pre-determined trajectory of the ion beam 10. Moreover, the first bar magnet 131 includes a first support rod 141 and a first winding coil 151, and the second bar magnet 132 includes a second support rod 142 and a second winding coil 152. Hence, when current I1 and/or I2 flows through the first bar magnet 131 and/or the second bar magnet 132 respectively, a magnetic field between the first bar magnet 131 and the second bar magnet 132 is generated which then affects the motion of ions.
FIG. 1C shows how the shape of the ion beam 10 is affected by the magnetic field between the first bar magnet 131 and the second bar magnet 132. As usual, the first winding coil 151 and the second winding coil 152 are uniformly distributed along the first support rod 141 and the second support rod 142, respectively, such that a continuous magnetic filed is formed, whereby the ion beam 10 can then be adjusted. Herein, each of the first/second support rod 141/142 is usually distributed along a direction intersecting with the ion beam travel direction. For example, the rod can be distributed along a direction perpendicular to the ion beam travel direction. Moreover, the continuous magnetic field essentially is a single-stage magnetic field because both the magnitude and the direction of the continuous magnetic field are gradually varied without any back and forth variation. When the currents I1 and I2 are parallel as shown in FIG. 1B, the magnetic fields generated by each bar magnet are generally opposite in direction in the space between the bar magnets. Significantly, the overall magnetic field contributed by both bar magnets points down near bar magnet 131, points up near bar magnet 132, points left toward magnet 131 in space below the center point, and points right toward bar magnet 132 in space above the center point. This is a typical quadrupole field. The quadrupole field can compress the ion beam in one direction and extend it in the other direction, depending on the relative direction between an ion beam and the bar magnets. When an ion beam 10 travels out of the paper in FIG. 1C, and the currents I1 and I2 flow in the direction shown in FIGS. 1B and 1C, the quadrupole field compresses the ion beam in the X direction and extends it in the Y direction, forming a beam narrower in the X direction and taller in the Y direction. When both currents I1 and I2 are reversed, the field extends the beam in the X direction and compresses it in the Y direction, forming a beam wider in the X direction and shorter in the Y direction.
However, for practical implantation requirements, the continuous magnetic field shown in FIG. 1C usually cannot effectively adjust the shape of the ion beam 10. In short, it only can smoothly change the ion beam shape between spot-shape and line-shape, but cannot strongly deform the ion beam shape because the corresponding winding coil and the support rod can change only the magnitude of the continuous magnetic field.
Therefore, as shown in FIG. 1D, yet another prior art approach was devised for adjusting the structure of both the first bar magnet 131 and the second bar magnet 132. In this case, the first bar magnet 131 includes a first support rod 141 and a plurality of winding coils 151/153/155. The winding coils 151/153/155 may be variably distributed along the first support rod 141. The second bar magnet 132 includes a second support rod 142 and a plurality of winding coils 152/154/156. The winding coils 152/154/156 also may be variably distributed along the second support rod 142. Power sources 161-166 are electrically coupled with the winding coils 151-156 respectively. Hence, when the real position/length of each of the winding coils 151-156 is variable and the power sources 161-166 are independently operable, it is possible to induce a multi-stage magnetic field wherein both the magnitude and the direction of the continuous magnetic field can be gradually varied with at least one back and forth oscillation. Therefore, owing to the fact that different portions of the ion beam may be affected by different portions of the multi-stage magnetic field, the shape of different portions of the ion beam 10 can be independently adjusted.
However, for practical implantation requirements, the multi-stage magnetic field shown in FIG. 1D usually is too complex and expensive to be used. In short, to the extent winding coils 151-156 and power sources 161-166 are provided with different configurations and currents such that multi-stage magnetic fields can be induced, the total mechanism and its proper operation may be too complex.
Because of disadvantages associated with the prior art mentioned above, a need exists to propose a novel ion implanter and a novel method for adjusting an ion beam so as to effectively and economically adjust the shape of an ion beam without having to substantially modify the conventional ion implanter.